Experiments on the Richtmyer–Meshkov instability: single-scale perturbations on a continuous interface

We report on experiments to measure the shock-induced growth of sinusoidal perturbations on thick interfaces separating two gases of different densities. The results show that the growth rates are reduced as the interface thickness is increased. A model that accounts for the growth rate reduction caused by the presence of a finite density gradient on the interface is proposed and good agreement is obtained with the experimental results

Experiments on the Richtmyer–Meshkov instability: Small-scale perturbations on a plane interface

This paper reports the results of measurements of the "visual thickness," obtained from flow visualization experiments by the schlieren method, of initially plane interfaces between two gases under impulsive accelerations. It is found that when such interfaces are processed by just one incident shock wave of strength of order Ms=1.5, their thickness increases slowly and they require observation over extended times; their growth rates are found to slow down with time, in agreement with simple theoretical arguments. The observed growth rates of thin interfaces formed by plastic membranes have been found to be substantially smaller than that reported by previous investigators. Also, thick, diffusively smoothed interfaces initially grow much more slowly than the discontinuous ones do. In these experiments, it is found that wall vortices formed by shock wave/boundary-layer interaction at the interface grow much more rapidly than the shock-processed interfaces in the bulk of the fluid. These wall structures can reduce the apparent growth of interfaces by vorticity-induced strain and impair the observation of the relevant interface phenomena

Heterogeneous Treatment and Self-Selection in a Wage Subsidy Experiment

The Self-Sufficiency Project (SSP) is a research and demonstration project that offered a generous time-limited income supplement to randomly selected welfare applicants under two conditions. The first, the eligibility condition, required that they remain on welfare for at least twelve months. The second, the qualification condition, required that they find a full-time job within twelve months after establishing eligibility. In this paper we focus on a neglected and important feature of the program, namely that the financial reward for becoming qualified is inversely related to the expected wage rate. Under very simple assumptions we show that those who have a low expected wage rate have a clear incentive to establish eligibility. Empirical non-parametric evidence strongly suggests that individuals self-select into eligibility. We jointly estimate a participation equation and a wage equation that are correlated through individual random effects. Our results show that the omission of self-selectivity into qualification translates into slightly overestimated treatment effects.SSP Applicant Study, heterogeneous treatment, self-selection

Les facteurs du déclin industriel de Shawinigan, province de Québec

Après avoir connu un essor industriel fulgurant au début du siècle, essor qui s'est poursuivi régulièrement pendant la première moitié du XXe siècle, la ville de Shawinigan a connu depuis les années 1950, et particulièrement depuis 1960, un déclin industriel marqué. L'indice de l'emploi manufacturier est passé de 100 en 1952 à moins de 60 en 1972, le groupe des produits chimiques ayant subi le gros des pertes. Plusieurs facteurs ont été avancés pour expliquer ce déclin : mauvais état des relations patronales-ouvrières, insuffisance de la promotion industrielle, nationalisation de l'électricité qui aurait pénalisé les régions périphériques productrices d'électricité au profit de Montréal, déficience du réseau de transport, etc. Cependant, à l'examen, il semble bien que, si tous ces facteurs ont eu leur importance dans la perte de poids qu'a subi l'industrie manufacturière de Shawinigan, le déclin doit être attribué principalement à la nature dynamique de la localisation industrielle, elle-même reliée au progrès technologique. Ainsi, en l'espace de vingt ans, les facteurs majeurs du développement industriel de Shawinigan, et plus généralement de la Mauricie, se sont modifiés et ne jouent plus le rôle attractif qu'ils jouaient auparavant. En conséquence, l'industrie shawiniganaise connaît de sérieuses difficultés.At the begining of the twentieth century, the town of Shawinigan, located in the province of Québec, was known for its spectacular industrial growth. This growth, which continued almost uninterrupted until the fifties, has given way to a steady decline since 1960. Owing largely to numerous layoffs in the chemical industries group, the manufacturing employment index (1952 = 100) dipped as low as 60 in 1972. Many reasons have been suggested to explain this decline : Militant labour unions have brought about an increase in production costs, industrial promotion has been insufficient, nationalization of power production facilities has favoured Montréal at the expense of peripheral power-producing regions, the transport network has become obsolete and congested, etc. Without discounting the importance of these factors, it seems that the decline of Shawinigan's manufacturing industry must be explained mainly in terms of the dynamics of industrial location, the latter being related to technological progress. Therefore, during the last two decades, the major factors of Shawinigan's industrial development have lost their importance and do not have the same attractive power as they used to. Consequently, Shawinigan has momentous problems in its industrial development